

import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.channels.spi.*;
import java.net.*;
import java.util.*;

// Listen on a port for connections and write back the current time.
public class NBTimeServer {
    private static final int DEFAULT_TIME_PORT = 8900;

    // Constructor with no arguments creates a time server on default port.
    public NBTimeServer() throws Exception {
	acceptConnections(this.DEFAULT_TIME_PORT);
    }

    // Constructor with port argument creates a time server on specified port.
    public NBTimeServer(int port) throws Exception {
	acceptConnections(port);
    }

    // Accept connections for current time. Lazy Exception thrown.
    private static void acceptConnections(int port) throws Exception {
	// Selector for incoming time requests
	Selector acceptSelector = SelectorProvider.provider().openSelector();

	// Create a new server socket and set to non blocking mode
	ServerSocketChannel ssc = ServerSocketChannel.open();
	ssc.configureBlocking(false);

	// Bind the server socket to the local host and port

	InetAddress lh = InetAddress.getLocalHost();
	InetSocketAddress isa = new InetSocketAddress(lh, port);
	ssc.socket().bind(isa);
	
	// Register accepts on the server socket with the selector. This
	// step tells the selector that the socket wants to be put on the
	// ready list when accept operations occur, so allowing multiplexed
	// non-blocking I/O to take place.
	SelectionKey acceptKey = ssc.register(acceptSelector, 
					      SelectionKey.OP_ACCEPT);
	
	int keysAdded = 0;
	
	// Here's where everything happens. The select method will
	// return when any operations registered above have occurred, the
	// thread has been interrupted, etc.
	while ((keysAdded = acceptSelector.select()) > 0) {
	    // Someone is ready for I/O, get the ready keys
	    Set readyKeys = acceptSelector.selectedKeys();
	    Iterator i = readyKeys.iterator();

	    // Walk through the ready keys collection and process date requests.
	    while (i.hasNext()) {
		SelectionKey sk = (SelectionKey)i.next();
		i.remove();
		// The key indexes into the selector so you
		// can retrieve the socket that's ready for I/O
		ServerSocketChannel nextReady = 
		    (ServerSocketChannel)sk.channel();
		// Accept the date request and send back the date string
		Socket s = nextReady.accept().socket();
		// Write the current time to the socket
                PrintWriter out = new PrintWriter(s.getOutputStream(), true);
		Date now = new Date();
		out.println(now);
		out.close();
	    }
	}
    }

    // Entry point.
    public static void main(String[] args) {
	// Parse command line arguments and
	// create a new time server (no arguments yet)
	try {
		NBTimeServer nbt = new NBTimeServer();
	} catch(Exception e) {
		e.printStackTrace();		
	}
    }
}
